Neuromyelitis optica spectrum disorder is a demyelinating disorder Overview of Demyelinating Disorders Most nerve fibers inside and outside the brain are wrapped with many layers of tissue composed of a fat (lipoprotein) called myelin. These layers form the myelin sheath. Much like the insulation... read more . It causes symptoms similar to those of multiple sclerosis Symptoms In multiple sclerosis, patches of myelin (the substance that covers most nerve fibers) and underlying nerve fibers in the brain, optic nerves, and spinal cord are damaged or destroyed. The cause... read more (MS) and used to be considered a variant of multiple sclerosis. However, neuromyelitis optica spectrum disorder typically affects mainly the eyes and the spinal cord, and multiple sclerosis also affects the brain.
The risk of becoming disabled is greater with neuromyelitis optica spectrum disorder than with multiple sclerosis. Thus, people with symptoms suggesting neuromyelitis optica spectrum disorder should see a doctor promptly.
Insulating a Nerve Fiber
Most nerve fibers inside and outside the brain are wrapped with many layers of tissue composed of a fat (lipoprotein) called myelin. These layers form the myelin sheath. Much like the insulation around an electrical wire, the myelin sheath enables nerve signals (electrical impulses) to be conducted along the nerve fiber with speed and accuracy. When the myelin sheath is damaged (called demyelination), nerves do not conduct electrical impulses normally.
Neuromyelitis optica spectrum disorder is also an autoimmune disorder Autoimmune Disorders An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues. What triggers autoimmune disorders is not known. Symptoms vary depending on... read more . Autoimmune disorders occur when the immune system malfunctions and attacks the body’s own tissues. In neuromyelitis optica spectrum disorder, the target of the autoimmune attack is a protein called aquaporin 4, which is present on the surface of support cells (called astrocytes) in the brain, spinal cord, and optic nerves. Damage to astrocytes is thought to lead to demyelination. In some people with neuromyelitis optica spectrum disorder, the immune system targets another protein called myelin oligodendrocyte glycoprotein (MOG), which is present on the outer layer of myelin.
Symptoms of NMOSD
Neuromyelitis optica spectrum disorder causes inflammation of the optic nerve ( optic neuritis Optic Neuritis Optic neuritis is inflammation of the optic nerve. Multiple sclerosis is the most common cause. Loss of vision may develop, and there may be pain with eye movement. Magnetic resonance imaging... read more ). One or both eyes may be affected. The disorder causes episodes of eye pain and dim, blurred, or lost vision.
Days to weeks (sometimes years) later, the limbs are affected. People may temporarily lose sensation. They may have painful muscle spasms, and the arms and legs may become weak and sometimes paralyzed. People may be unable to control the bladder ( urinary incontinence Urinary Incontinence in Adults Urinary incontinence is involuntary loss of urine. Incontinence can occur in both men and women at any age, but it is more common among women and older people, affecting about 30% of older women... read more ) and bowels ( fecal incontinence Fecal Incontinence Fecal incontinence is the loss of control over bowel movements. Fecal incontinence can occur briefly during bouts of diarrhea or when hard stool becomes lodged in the rectum ( fecal impaction)... read more ).
In some people, the part of the spinal cord that controls breathing is inflamed, leading to difficulty breathing, which is life threatening.
Neuromyelitis optica spectrum disorder progresses differently in each person. As the disorder progresses, people may have brief, frequent, painful muscle spasms. Eventually, blindness, loss of sensation and muscle weakness in the limbs, and bladder and bowel dysfunction may become permanent.
Diagnosis of NMOSD
A doctor's evaluation
Magnetic resonance imaging
To diagnose neuromyelitis optica spectrum disorder, doctors evaluate the nervous system ( neurologic examination Neurologic Examination When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the nervous system. Examination of the nervous system—the... read more ) during a physical examination. The optic nerve is examined with an ophthalmoscope What Is an Ophthalmoscope? .
Usually, tests include magnetic resonance imaging (MRI) of the brain to rule out multiple sclerosis. MRI of the spinal cord and evoked responses Evoked Responses Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Electroencephalography (EEG) is a simple, painless procedure in which... read more are done to help confirm the diagnosis of neuromyelitis optica spectrum disorder.
When the evoked responses test is used to diagnose neuromyelitis optica spectrum disorder, stimuli for sight (such as a flashing light) are used to activate certain areas of the brain. Then, electroencephalography Electroencephalography Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Electroencephalography (EEG) is a simple, painless procedure in which... read more is used to detect the response to the stimuli. Based on these responses, doctors can tell how well the optic nerve is working.
Blood tests to detect specific antibodies to aquaporin 4 and to myelin oligodendrocyte glycoprotein may be done to distinguish neuromyelitis optica spectrum disorder from multiple sclerosis. ( Antibodies Antibodies One of the body's lines of defense ( immune system) involves white blood cells (leukocytes) that travel through the bloodstream and into tissues, searching for and attacking microorganisms and... read more are proteins produced by the immune system to help defend the body against a particular attacker.)
Treatment of NMOSD
Drugs that suppress the immune system
There is no cure for neuromyelitis optica spectrum disorder. However, treatments can stop episodes, control symptoms, and prevent episodes from recurring.
A corticosteroid (such as methylprednisolone) and a drug that suppresses the immune system (an immunosuppressant, such as azathioprine) are often used to stop and prevent episodes.
Rituximab (a monoclonal antibody Monoclonal Antibodies Immunotherapy is the use of drugs that mimic or modify components of the immune system (such as tumor antigens and immune checkpoints—see also Overview of the Immune System) to fight disease... read more used as an immunosuppressant) may be used to reduce the number of abnormal antibodies and to control the disorder.
Eculizumab (another monoclonal antibody) can sometimes help. This drug suppresses complement, which is a component of the immune system. Side effects of this drug include life-threatening meningococcal meningitis Meningococcal Infections Meningococcal infections are caused by the bacteria Neisseria meningitidis (meningococci) and include meningitis and sepsis. Infection is spread by direct contact with nasal and throat... read more , pneumonia, upper respiratory infections, and headache. Doctors usually give people who take eculizumab the meningococcal vaccine Meningococcal Vaccine The meningococcal vaccine protects against infections caused by the bacteria Neisseria meningitidis (meningococci). Meningococcal infections can lead to meningitis (an infection of tissue... read more and closely monitor them.
Satralizumab and inebilizumab (both monoclonal antibodies) can be used to treat neuromyelitis optica spectrum disorder when aquaporin-4 antibodies are present. People taking these drugs are closely monitored for infections, such as urinary tract and respiratory infections.
Plasma exchange Plateletpheresis (platelet donation) In addition to normal blood donation and transfusion, special procedures are sometimes used. In plateletpheresis, a donor gives only platelets rather than whole blood. Whole blood is drawn from... read more may help people who do not respond to corticosteroids. For this treatment, blood is removed, then abnormal antibodies are removed, and the blood is returned to the person.
Treatment of symptoms Symptom control In multiple sclerosis, patches of myelin (the substance that covers most nerve fibers) and underlying nerve fibers in the brain, optic nerves, and spinal cord are damaged or destroyed. The cause... read more is similar to that for multiple sclerosis. Baclofen or tizanidine may relieve muscle spasms.